Because of their unique sieving characteristics, as well as their catalytic properties, crystalline molecular sieves and zeolites are especially useful in applications such as hydrocarbon conversion, gas drying and separation. Although many different crystalline molecular sieves have been disclosed, there is a continuing need for new molecular sieves with desirable properties for gas separation and drying, hydrocarbon and chemical conversions, and other applications. New molecular sieves can contain novel internal pore architectures, providing enhanced selectivities in these processes.
Molecular sieves have been conventionally prepared by hydrothermal synthesis, wherein an aqueous reaction mixture containing a tetrahedral atom source(s), a mineralizer, and a structure directing agent is heated under autogenous pressure in an autoclave. More recently, it has been reported that molecular sieves can be prepared by ionothermal synthesis, wherein an ionic liquid is used as both the solvent and the structure directing agent (“SDA”), also known as a crystallization template (see, e.g., E. R. Cooper et al., Nature 2004, 430, 1012-16; and E. R. Parnham et al., J. Am. Chem. Soc. 2006, 128, 2204-2205). Ionic liquids are a class of compounds made up entirely of ions and are generally liquids at ambient and near ambient temperatures. Ionic liquids tend to be liquids over a very wide temperature range, with some having a liquid range of up to 300° C. or higher. Ionic liquids are generally non-volatile, with effectively no vapor pressure. Many are air and water stable, and can be good solvents for a wide variety of inorganic, organic, and polymeric materials.
Ionothermal synthesis of molecular sieves has several advantages over conventional hydrothermal synthesis. Safety concerns associated with operating under high pressures during hydrothermal synthesis are eliminated. Since most ionic liquids are generally non-volatile, with effectively no vapor pressure, no autogenous pressure is produced on heating thereby allowing molecular sieve synthesis to take place at high temperature while keeping the pressure at ambient levels. Moreover, the ionic liquid used in ionothermal synthesis can be recycled for further use.